The present invention relates to an anti-loosening nut assembly.
The present applicant has developed an anti-loosening nut assembly, each of them comprising a lower nut with a protrusion and an upper nut with a recess. The protrusion and the recess are shaped comple-mentarily so that the protrusion is received in the recess in such an eccentric manner as surely protecting the double-nut from any inadvertent loosening. In detail, both the lower and upper nuts have threaded bores extending therethrough, and the protrusion from the lower nut has around the threaded bore an outer periphery that is tapered to reduce its diameter towards the outer end of the lower nut. The outer periphery of said protrusion is shaped slightly eccentric with respect to the lower nut""s threaded bore. On the other hand, the recess formed in the upper nut to fit on such a protrusion has an inner periphery that is formed coaxial with the upper nut""s threaded bore. Thus, an eccentric relationship is provided between the protrusion and the recess. If and when those nuts are fastened to each other, they will be forced sideways a small radial distance away from the common axis of the threaded bores. Consequently, strong stresses will be imparted in opposite radial directions to a threaded rod or bolt body engaging with the threaded bores. Such a combination of strong stresses is sometimes called a xe2x80x98wedgingxe2x80x99 effect of firmly retaining those nuts in position, without allowing any inadvertent loosening thereof.
Among various types of fastening tools available for use, box wrenches easy to handle for quick operations have widely been preferred. However, in case of tightening the xe2x80x98upperxe2x80x99 nut of the anti-loosening nut assembly with use of the box wrench, it has been likely to undesirably engage with the xe2x80x98lowerxe2x80x99 nut that had previously and smoothly been set in position. In such an event, the upper nut would not be rotated relative to the lower nut, failing to afford the xe2x80x98wedgingxe2x80x99 effect and disabling the nut assembles anti-loosening function.
It is also noted that, for ensuring the anti-loosening effect, both the lower and upper nuts of each nut assembly have to be tightened with a proper torque. Therefore, some types of torque wrenches preset to exert a prescribed torque have sometimes been used, confirming its instant level during the tightening work. However, workers would not be able to employ such a torque wrench where it could not operate smoothly. Accordingly, they would have to use any single-ended or other ordinary spanner instead of the torque wrench, being obliged to work relying on their experience and/or perception. In these cases of tightening the anti-loosening nut assemblies, the proper torque would often be unrealized, or the spanner would possibly slip down to the lower nut from the upper nut just being screwed. Joint rotation of the upper and lower nuts, or the like undesired interaction between them, will result in an unsatisfactory setting of the nut assembly.
In view of these problems, an object of the present invention is to provide an anti-loosening nut assembly whose constituent nuts can easily and surely be tightened at a proper fastening torque, even without use of any torque wrench.
The anti-loosening nut assembly proposed herein consists essentially of an upper nut and a lower nut, one of the nuts having around a threaded bore thereof a protrusion shaped to fit into a recess that is formed in the other nut around a threaded bore thereof. The protrusion of the one nut has an outer periphery tapered such that its diameter decreases outwards in axial direction towards the other nut. One periphery selected from the outer periphery of the protrusion and an inner periphery of the recess is formed slightly eccentric with respect to the corresponding threaded bore, with the other of the peripheries being formed coaxial with the corresponding threaded bore.
The upper nut may preferably comprise at least one lateral lug protruding sideways therefrom. The at least one lug will bear against the lower end portion (such as the lower surface or the inner peripheral end region surrounding a nut-engaging cavity) of a spanner, a box wrench or the like fastening tool when it is used to tighten the upper nut. The lateral lug or lugs may be shaped such that its or their angle of rotation can visually be detected.
In use of the nut assembly provided herein as just summarized above, the lateral lug or lugs will bear against the fastening tool when the latter tightens the upper nut. The fastening tool will be protected from any undesired interference or engagement with the lower nut, and thus can easily tighten the upper nut. As visual detection of the rotation angle of the upper nut is now so facilitated that it can be tightened exactly while checking a torque that is being applied thereto.
From another aspect, the present invention provides an anti-loosening nut assembly consisting essentially of an upper nut and a lower nut, one of the nuts having around a threaded bore thereof a protrusion shaped to fit into a recess formed in the other nut around a threaded bore thereof. The protrusion of the one nut has an outer periphery tapered such that its diameter decreases outwards in axial direction towards the other nut. One periphery selected from the outer periphery of the protrusion and an inner periphery of the recess is formed slightly eccentric with respect to the corresponding threaded bore, with the other of the peripheries being formed coaxial with the corresponding threaded bore. Characteristically, the upper nut comprises at least one lateral lug protruding sideways from a lower portion (portions) of the outer periphery so as to bear against the lower end portion of a fastening tool when it is used to tighten the upper nut.
In use of the nut assembly of the type just mentioned above, the lateral lug or lugs of the upper nut will bear against the fastening tool when the latter tightens it. The fastening tool will be protected from any undesired interference or engagement with the lower nut, and thus can easily tighten the upper nut. The lateral lug or lugs protruding from the lower peripheral portion (portions) of the upper nut does facilitate visual detection of the rotation angle of the upper nut so that it can be tightened exactly while checking a torque that is being applied thereto.
The lateral lug or lugs may protrude from the upper nut""s outer and vertical surface that will be pressed on the inner surface of a spanner or the like fastening tool for tightening the upper nut. In this case, the lug is or lugs are made firmly integral with the body of the upper nut, while more easily manufacturing same. Configuration of the lug or lugs can be designed in any proper fashion, and for example it or they may form a flange extending all around the upper nut. An embossed marking, a projection or a notch may be formed in or on the circumferential flange at any proper point thereof, for the purpose of visually sensing the rotation angle.
In the present invention, the lateral lug or lugs protruding from the upper nut body will serve on one hand for control of the torque being applied thereto, and also serve on the other hand as a stopper inhibiting the fastening tool from making any excessive displacement beyond a limit in an axial direction along the nut body. Thus, in spite of such a considerable simple structure as simplifying the molds for manufacture of the nut assembly, the present invention affords visual sensing of the tightening torque as well as improvement in easiness and exactness of the fastening operation. The lateral lug or each lateral lug may be designed to have a protuberance portion jutting outwards in radial direction beyond the outer edge of each corner of the lower nut. This structure will be effective to prevent the lug or lugs from being forced into the box-shaped cavity in a box wrench, even if the latter is of the dodecagonal shape. Preferably, a distance between the axis of the upper nut and the outer tip end of each radially extending lug of this nut (viz., maximum radius of the lug or the lugs as a whole) is made equal to or greater than the maximum radius of the lower nut (viz., a distance between the axis and each of six corners, in case of a hexagonal nut). The lower nut may have a diameter equal to or greater than that of the upper nut.
Both the upper and lower nuts may be hexagonal nuts, and preferably in this case the at least one lateral lug may be formed at the lower end portion of at least one of six corners possessed by the upper nut. Such a structure will enable the lug or lugs to be mechanically processed at a location remote from the central protrusion or central recess eccentrically fitting thereon. This means that the machining of those lugs will be rendered easier and they can be formed without substantially sacrificing the rigidity of material adjacent to the protrusion or recess. By virtue of this feature, a tight and firm eccentric engagement of the protrusion with the recess will be ensured, without any fear of impairing the requisite anti-loosening effect. Further, at least one of the six corners may be left devoid of the lateral lug so that the lateral lugs formed at the other corners can serve as an apparent xe2x80x98yardstickxe2x80x99 denoting the rotation angle but not likely to be mistaken by a fastening operator, thereby allowing him or her to visually and readily control the torque being applied to the nut. Also preferably, the lateral lug or lugs may be provided by striking upwards the upper nut corners at lower end faces thereof. The lower end portions of such corners will thus be plastically deformed outwards in radial direction. In this case, raw xe2x80x98hard lock nutsxe2x80x99 may be prepared using any proper and conventional press known in the art, before their lower ends are struck with a proper hammering machine to easily and quickly form the lateral lug or lugs. The xe2x80x98hard lock nutsxe2x80x99 finished in this way at a suppressed additional manufacturing cost will nevertheless show an excellent behavior in use and enable visual control of the fastening torque.